The use of pump rod clamps and blowout preventers on oil, gas and water wells is a common occurrence. Pump rod clamps are used generally to hold the pump or polished rod and may take any one of a wide variety of forms ranging from a pair of rams that are driven radially inward in order to contact the pump rod and hold it in place, to wedges that may be inserted around the rod, to a pair of clamping members that may be bolted around the exterior surface of the rod and hung from a mandrel or other support member. Regardless of the particular structure of the clamp, its primary purpose is to either suspend the rod within the well, and/or to prevent rotational movement of the pump rod.
Blowout preventers (or BOP's as they are typically called) are critical pieces of equipment that are used to seal off the well and contain its contents under a variety of different situations. For example, during the servicing of a wellhead one or more blowout preventers are often used to seal against the pump or polished rod to contain the contents of the well when downstream equipment is removed or disassembled for servicing. In other instances blowout preventers may be used to seal off a well where the pump rod is removed, or in the event of a failure of the pump rod.
Blowout preventers that are used in producing oil and gas wells are most commonly comprised of a pair of rams that are received within cylinders or bores extending through a BOP housing and situated generally perpendicular to the longitudinal axis of the well casing. Typically the end of each ram has a semi-circular channel on its face to allow it to seal against the exterior surface of the polished rod when driven inwardly. The faces of the rams may include an elastomer or other sealing mechanism to ensure that a fluid tight seal is created when the rams fully engage the polished rod. Examples of such prior existing blowout preventers are described in U.S. Pat. Nos. 4,860,826, 5,746,249, and 5,875,841.
While currently available blowout preventers are generally effective in sealing around a polished rod and preventing the contents of a well from escaping, they nevertheless suffer from a number of inherent limitations. In order to ensure a tight seal between the rams and the polished rod, particularly where the well is a high pressure well or contains natural gas or hydrogen sulfide, operators have developed a tendency to drive the rams inwardly against the polished rod using a considerable amount of force. While doing so has the effect of compressing the elastomer against the rod and helping to ensure a good seal, in many cases the metal faces of the rams are also driven into contact with the exterior surface of the rod. In some cases rig hands intentionally drive the faces of the rams into the polished rod as a means to not only seal off the well, but to also effectively act as a rod clamp to hold the polished rod in place. Where the pump in question is a reciprocating pump, the rams may be used to maintain or hold the weight of the rod while work is performed upon components downstream of the BOP. Where the pump is a rotary style pump, the rams may be used to both hold the weight of the polished rod and to prevent rotation caused through backspin forces applied to the rotor of the pump by the head of fluid in the well. In either case, use of the BOP rams to not only seal the well but to grasp or clamp the rod can have the effect of marking or scoring the exterior surface of the rod and/or the face of the ram, neither of which is desirable. Further, when the metallic faces of the rams contact the exterior of the polished rod an electrical connection will be formed therebetween, which in some circumstances may also be undesirable.
Currently available polished rod clamps are also not without their limitations. Where the well is equipped with a separate polished rod clamp the overall height of the wellhead will be increased by the height of the clamp. Use of a dedicated rod clamp also results in an increase in equipment cost and represents a further mechanical component that may malfunction or fail. In addition, the use of a separate polished rod clamp does not prevent an operator from over tightening the BOP rams and causing their metal faces to score or damage the surface of the polished rod.